Refactor AST and Parser into modular subdirectories

- Split ast.h into granular headers in v0/ast/
- Split parser.c into modular implementation files in v0/parser/
- Move and rename parser tests to v0/parser/test_*.c
- Update build system (include.mk) with modular sub-makefiles
- Maintain v0/ast.h and v0/parser.h as umbrella headers

v0/parser/internal.h

@@ -0,0 +1,37 @@
+#ifndef PARSER_INTERNAL_H
+#define PARSER_INTERNAL_H
+
+#include "../parser.h"
+#include "../token.h"
+#include "../ast.h"
+
+typedef struct {
+    TokenStream* ts;
+    Token token;
+} Parser;
+
+// Core functions
+void parser_next_token(Parser* p);
+bool parser_accept(Parser* p, TokenType token);
+bool parser_expect(Parser* p, TokenType token, const char* msg);
+bool parser_peek(Parser* p, TokenType token);
+bool parser_require(Parser* p, TokenType token, const char* msg);
+char* parser_to_text(Parser* p);
+bool parser_accept_primitive(Parser* p);
+
+// Base parsing (expressions, types)
+bool parse_primitive_type_expression(Parser* p, TypeExpression* expr);
+bool parse_array_type_expression(Parser* p, TypeExpression* expr);
+bool parse_type_expression(Parser* p, TypeExpression* expr);
+bool parse_expression(Parser* p, Expression* expr);
+void free_type_expression(TypeExpression* expr);
+
+// Declaration parsing
+bool parse_import_declaration(Parser* p, Module* module, bool is_public);
+bool parse_alias_declaration(Parser* p, Module* module, bool is_public);
+bool parse_variable_declaration(Parser* p, Module* module, bool is_public, bool is_static, bool is_const);
+
+// Module parsing
+bool parse_module_declaration(Parser* p, Module* module);
+
+#endif